Visualizations of Quantum Chromodynamics

This page provides a collection of the most recent visualizations
of Quantum Chromodynamics (QCD), the underlying theory of the
strong interactions. As a key component of the Standard Model of
the Universe, QCD describes the interactions between quarks and
gluons as they compose particles such as the proton or neutron.

State of the art order a4-improved lattice operators
are used in creating the animations, including the three-loop
improved lattice gauge action and the five-loop improved lattice
field strength tensor.

The animations to the right and above illustrate the typical
four-dimensional structure of gluon-field configurations averaged
over in describing the vacuum properties of QCD. The volume of
the box is 2.4 by 2.4 by 3.6 fm, big enough to hold a couple of
protons. Contrary to the concept of an empty vacuum, QCD induces
chromo-electric and chromo-magnetic fields throughout space-time
in its lowest energy state. After a few sweeps of smoothing the
gluon field (50 sweeps of APE smearing), a lumpy structure
reminiscent of a lava lamp is revealed. This is the QCD Lava
Lamp. The action density (top) and the topological charge
density (right) are displayed. The former is similar to an
energy density while the latter is a measure of the winding of
the gluon field lines in the QCD vacuum.

This animation shows the suppression of the QCD vacuum from the
region between a quark-antiquark pair illustrated by the coloured
spheres. The separation of the quarks varies from 0.125 fm to
2.25 fm, the latter being about 1.3 times the diameter of a
proton. The surface plot illustrates the reduction of the vacuum
action density in a plane passing through the centers of the
quark-antiquark pair. The vector field illustrates the gradient
of this reduction. The tube joining the two quarks reveals the
positions in space where the vacuum action is maximally expelled
and corresponds to the famous "flux tube" of QCD. As the
separation between the quarks changes the tube gets longer but
the diameter remains approximately constant. As it costs energy
to expel the vacuum field fluctuations, a linear confinement
potential is felt between quarks.

The manner in which QCD vacuum fluctuations are expelled from the
interior region of a baryon like the proton is animated at right.
The positions of the three quarks composing the proton are
illustrated by the coloured spheres. The surface plot
illustrates the reduction of the vacuum action density in a plane
passing through the centers of the quarks. The vector field
illustrates the gradient of this reduction. The positions in
space where the vacuum action is maximally expelled from the
interior of the proton are also illustrated by the tube-like
structures, exposing the presence of flux tubes. A key point of
interest is the distance at which the flux-tube formation occurs.
The animation indicates that the transition to flux-tube
formation occurs when the distance of the quarks from the centre
of the triangle (&lt r &gt) is greater than 0.5 fm. Again, the
diameter of the flux tubes remains approximately constant as the
quarks move to large separations. As it costs energy to expel
the vacuum field fluctuations, a linear confinement potential is
felt between quarks in baryons as well as mesons.

Strange quarks play an important role in the structure of the
proton. This artistic rendition provides a modern interpretation of
the composition of a proton and how expermentalists probe its
structure through electron scattering.